Electromagnetic compatibility gasket and vent

ABSTRACT

A chassis-mounted electronic device includes a chassis, an upper EMI gasket, and a lower EMI gasket is provided. The chassis, including an upper chassis and a lower chassis, is constructed from a conductive sheet with a first thickness. The upper chassis and the lower chassis are coupled to form an interior of the chassis housing an electronic device. The upper EMI gasket is attached to the upper chassis, and is thinner than the upper chassis. The lower EMI gasket is attached to the lower chassis, and is also thinner than the lower chassis. The upper and lower EMI gaskets include perforations to allow cooling air through the EMI gaskets and into the interior of the chassis. Both the upper EMI gasket and the lower EMI gasket are configured to resiliently contact a portion of the electronic device to provide EMI shielding for the electronic device.

TECHNICAL FIELD

The present disclosure relates to cooling and electromagneticcompatibility of electronic devices.

BACKGROUND

Chassis-mounted electronic devices, such as network equipment, typicallybring a large number of electronic devices in close proximity, which maylead to issues with heat management and Electro-Magnetic Interference(EMI) management. The heat generated by the chassis-mounted electronicdevices is typically managed by drawings cooling air through thechassis, which is most effective with large open spaces in the chassis.In contrast, EMI management relies on the chassis providing a Faradaycage to contain stray electromagnetic emitted from the electronicdevices in the chassis, which is compromised by large openings in thechassis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an electronic device configured with an EMIgasket, according to an example embodiment.

FIG. 2 is a side view of an electronic device that illustrates theairflow through the device, according to an example embodiment.

FIG. 3A illustrates an EMI gasket that enables increased airflow,according to an example embodiment.

FIGS. 3B and 3C show cross-sectional views of an EMI gasket, accordingto example embodiments.

FIG. 4 illustrates the attachment of an upper EMI gasket to an upperchassis, according to an example embodiment.

FIG. 5 illustrates the attachment of a lower EMI gasket to a lowerchassis, according to an example embodiment.

FIG. 6 is a flowchart illustrating operations for assembling anelectronic device in a chassis with EMI gaskets, according to an exampleembodiment.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

In one form, an apparatus is provided comprising a chassis, an upper EMIgasket, and a lower EMI gasket is provided. The chassis comprises anupper chassis and a lower chassis that are constructed from a conductivesheet with a first thickness. The upper chassis and the lower chassisare coupled to form an interior of the chassis housing an electronicdevice. The upper EMI gasket is attached to the upper chassis, and has asecond thickness that is less than the first thickness. The upper EMIgasket includes perforations to allow cooling air through the upper EMIgasket and into the interior of the chassis. The lower EMI gasket isattached to the lower chassis, and also has a second thickness that isless than the first thickness. The lower EMI gasket includesperforations to allow cooling air through the lower EMI gasket and intothe interior of the chassis. Both the upper EMI gasket and the lower EMIgasket are configured to resiliently contact a portion of the electronicdevice to provide EMI shielding for the electronic device.

Example Embodiments

As the market for chassis-mounted electronic devices, such as networkswitches and routers, progresses into producing higher volumes, thelandscape for providing an enterprise switch moves from simply providingperformance and features to incorporating a measure of value and cost.In a high volume manufacturing environment, a relatively small cost toadd a feature to a single unit can lead to significant costs whenmultiplied over a yearlong manufacturing run. Leveraging and reusingcommon units, such as fans, heatsinks, and power supplies, may providecost savings, but indirectly lead to a thermal bottleneck when a systemis upgraded with a next generation, high heat flux Application SpecificIntegrated Circuit (ASIC). In addition to generating additional heat,smaller and denser ASICs may have stricter constraints on a maximumlong-term temperature. The combination of denser ASICs and the reuse ofcommon units designed for previous generations lead to thermalchallenges. The techniques described herein provide for increasedairflow to deal with the increased heat in a cost effective manner,rather than redesigning the commonly used fan units or applying exoticheat sink solutions.

Additionally, a manual assembly line presents a challenge to loweringthe unit cost of high volume manufacturing due to the overhead burdenand quality issues, such as human error. Automation of an assembly lineaims to mitigate human factors in the assembly line to reduce the unitcost in a high volume manufacturing environment. The techniquesdescribed herein enable increased automation in the assembly ofchassis-mounted electronic devices by reducing the complexity of theassembly process (e.g., replacing complex placement of components infavor of linear pick and place motion).

Existing solutions for increasing the airflow through a chassis-mountedelectronic device (e.g., slanting the faceplate of the chassis toprovide more vent holes, precision machining to increase the percentageof the front faceplate that can open for vent holes, or directingairflow through larger openings in the faceplate and additional smallervent holes within the chassis) present additional constraints in costand ease of manufacturing. Exotic solutions to thermal management (e.g.,vapor chambers or three dimensional heat pipes) typically raise the costof producing the chassis-mounted device to unprofitable levels.

Referring now to FIG. 1, a chassis-mounted network device 100 is shown.Though the figures presented herein describe a network device, anychassis-mounted electronic device may benefit from the techniquesdescribed herein, and the specific embodiment of a chassis-mountednetwork device is used as an example. The network device 100 includeselectronics 110 that are enclosed within the chassis 120 and ports 115that provide access to the enclosed electronics 110 from outside thechassis 120.

In the magnified portion of FIG. 1, the chassis 120 has made transparentfor clarity in depicting additional portions of the network device 100.An upper Electro-Magnetic Interference (EMI) gasket 130 is shown thatconnects the frame of the ports 115 to the chassis. A lower EMI gasket140 also connects the frame of the ports 115 to the chassis. The upperEMI gasket and the lower EMI gasket 140 include perforations that allowcooling air to enter the chassis 120 above and below the ports 115.Bolts 150 securely connect the portions of the network device 100 withinthe chassis 120. Once the bolts 150 have fastened the upper EMI gasket130, the lower EMI gasket 140, and the ports 115 to the chassis 120, aFaraday cage encloses the electronics 110 and mitigates strayelectromagnetic radiation from the electronics 110.

In one example, the chassis 120 may be split into an upper chassis and alower chassis that are fastened together to provide structural supportfor the electronics 110. The chassis 120 may be manufactured from sheetsof conductive material (e.g., stainless steel) to form a portion of aFaraday cage providing EMI shielding for the electronics 110.Additionally, the chassis 120 may include standoffs to support one ormore boards of the electronics 110 or other components housed within thechassis 120. The material of the sheet(s) forming the chassis 120 is ofsufficient thickness (e.g., 2 mm of stainless steel) to providestructural support for the network device 100.

In another example, the upper EMI gasket 130 and the lower EMI gasket140 may be manufactured from a sheet of relatively thin conductivematerial (e.g., 0.25 mm of stainless steel) in comparison to the sheetmaterial forming the chassis 120. Perforations may be stamped into theupper EMI gasket 130 and the lower EMI gasket 140 to allow cooling airto flow into the interior of the chassis 120. The upper EMI gasket 130and the lower EMI gasket 140 may also be curved to provide a springresilience between the chassis 120 and the frame of the ports 115 whenthe chassis 120 is assembled.

Referring now to FIG. 2, a side view of the network device 100 is shownwith an example of the airflow through the interior of the chassis 120cooling the electronics 110. A portion of the electronics 110 aredisposed on a main board 210 enclosed completely by the chassis 120.Another portion of the electronics 110 are disposed on a daughtercard220 that includes the ports 115. A fan 230 draws air through the upperEMI gasket 130 and the lower EMI gasket 140 into the interior of thechassis 120.

The magnified portion of FIG. 2 illustrates specific features of thechassis support and airflow through the front of the network device 100.The chassis 120 includes an upper standoff 240 and a lower standoff 245that are configured to position the ports 115 on the daughtercard 220 toallow airflow above and below the daughtercard 220. In one example, theupper standoff 240 is manufactured from the same material as the uppercomponent of the chassis 120. Similarly, the lower standoff 245 may bemanufactured from the same material as the lower component of thechassis 120. The upper EMI gasket 130 and the lower EMI gasket 140(shown in cross-section in FIG. 2) are curved to allow the air to flowthrough the EMI gaskets in multiple locations and directions. Thecurved-cross section of the EMI gaskets also provides a spring force toensure good electrical contact between the chassis 120 and the framesurrounding the ports 115. In another example, the main board 210 may bepositioned away from the front of the network device 100 to prevent themain board 210 from constricting the air flowing through the lower EMIgasket 140.

Referring now to FIG. 3A, an example of an EMI gasket 300 is shown. TheEMI gasket 300 may be the upper EMI gasket 130 or the lower EMI gasket140, as shown in FIG. 1 and FIG. 2. The EMI gasket 300 includesperforations 310 separated by a web 320 of metal. The EMI gasket 300also includes fingers 330 configured to contact the frame of theelectronics extending out of the chassis (e.g., ports 115) at multiplepoints to ensure good electrical contact along the length of the EMIgasket 300. The EMI gasket 300 further includes at least one space 340to allow a connecting bolt (e.g., bolt 150 shown in FIG. 1) to securethe chassis in place around the electronic components.

In one example, the EMI gasket 300 may be manufactured by punching theperforations 310 from a thin metal strip. In typical sheet metalmanufacturing process, the width of the web 320 is constrained by thethickness of the base sheet metal to ensure the integrity of thefinished product. For instance, the web 320 may be constrained to beingapproximately twice the thickness of the sheet metal. The EMI gasket 300may be made from a sheet metal that is sufficiently thin to allow theperforations 310 to cover at least 90% of the EMI gasket 300. Incontrast, the chassis provides structural support for the entire device,and is manufactured from thicker sheet metal. The thinner sheet metal ofthe EMI gasket enables a thinner web 320 than an array of vent holespunched into the chassis itself, and allows for a greater surface areato be covered with perforations 310.

In another example, the EMI gasket 300 is curved to provide a springresilience between the chassis (e.g., chassis 120) and the frame of theelectronics extending out of the chassis (e.g., ports 115). The curve inthe EMI gasket may be discrete or continuous, and may include convex orconcave shapes. FIG. 3B shows a cross-sectional view of one example ofthe curve in the EMI gasket 300. FIG. 3C shows a cross-sectional view ofanother example of a more complex curve in the EMI gasket 300. Referringback to FIG. 1 and FIG. 2, the curve in the upper EMI gasket 130 may bedifferent than the curve in the lower EMI gasket 140. Alternatively, thetwo EMI gaskets may have the same cross-sectional curve.

Turning now to FIG. 4, an example of pre-mounting the upper EMI gasket130 on the chassis is shown. Before the chassis-mounted electronicdevice (e.g., network device 100 shown in FIG. 1) is assembled, theupper EMI gasket 130 is attached to an upper chassis 410. The upperchassis 410 includes standoffs 420 that position the electronics thatextend out of the chassis (e.g., ports 115 shown in FIG. 1). As shown inthe magnified portion of FIG. 4, the upper EMI gasket 130 is fastened tothe upper chassis 410 through the standoffs 420. The standoffs 420include a slot 430 that matches a locking tab 440 that is formed on theupper EMI gasket 130. Additional support for the upper EMI gasket 130 isprovided by fingers 450, which are part of the upper chassis 410.

Referring to FIG. 5, an example of pre-mounting the lower EMI gasket 140on a lower chassis 510 is shown. The lower EMI gasket 140 is placed onthe lower chassis 510 and held in place by a chassis bracket 520. Thechassis bracket 520 includes standoffs 530 that position the electronicsthat extend out of the chassis (e.g., ports 115 shown in FIG. 1). Asshown in the magnified portion of FIG. 5, a swaged connection 540fastens the chassis bracket 520 to the lower chassis 510 and secures thelower EMI gasket 140 between the chassis bracket 520 and the lowerchassis 510.

Combining the upper chassis 410 shown in FIG. 4 (i.e., pre-mounted withthe upper EMI gasket 130) with the lower chassis 510 shown in FIG. 5(i.e., pre-mounted with the lower EMI gasket 140) enables a simplifiedassembly process of the network device shown in FIG. 1. With thepre-assembled chassis components, the final assembly of the chassis maybe completed with pick and place automation. This automation removeshuman factors and leads to higher quality and lower unit cost of theelectronic device.

Referring now to FIG. 6, a flowchart is shown that depicts operations inan example process 600 of assembling a chassis-mounted electronicdevice. At 610, an electronic device is mounted on a lower chassisconstructed of a conductive sheet of a first thickness. In one example,the lower chassis is constructed primarily from a stainless steel sheetthat is approximately 2 mm thick. Alternatively, the lower chassis maybe constructed from other materials (e.g., aluminum) with a range ofthicknesses (e.g., 1-5 mm) that is sufficient to provide structuralsupport to the electronic device.

At 620, a lower EMI gasket is attached to the lower chassis. The lowerEMI gasket has a second thickness that is less than the first thickness.In one example, the lower EMI gasket may be constructed from a sheet ofstainless steel that is approximately 0.25 mm thick. Additionally, thelower EMI gasket includes perforations to allow cooling air through thelower EMI gasket. In one example, the perforations cover at least 90% ofthe lower EMI gasket to ensure sufficient airflow to cool the electronicdevice.

At 630, an upper EMI gasket is attached to an upper chassis. The upperchassis has a first thickness to provide structural support for theassembled electronic device. In one example, the upper chassis isconstructed primarily from a stainless steel sheet that is approximately2 mm thick. Alternatively, the upper chassis may be constructed fromother materials (e.g., aluminum) with a range of thicknesses (e.g., 1-5mm) that is sufficient to provide structural support to the electronicdevice. The upper EMI gasket has a second thickness that is less thanthe first thickness. In one example, the upper EMI gasket may beconstructed from a sheet of stainless steel that is approximately 0.25mm thick. Additionally, the upper EMI gasket includes perforations toallow cooling air through the upper EMI gasket. In one example, theperforations cover at least 90% of the upper EMI gasket to ensuresufficient airflow to cool the electronic device.

At 640, the upper chassis and the lower chassis are coupled together toenclose the electronic device. The upper EMI gasket and the lower EMIgasket are configured to resiliently contact a portion of the electronicdevice to provide EMI shielding for the electronic device, whileallowing cooling air to pass through the perforations in the upper EMIgasket and the lower EMI gasket. In one example, the upper chassis andlower chassis are connected by bolts that are electrically connected tothe upper EMI gasket and the lower EMI gasket. The bolts connecting theupper chassis and the lower chassis may be conductive to provide furtherEMI shielding to the electronic device.

In summary, the techniques presented herein provide a system layout thatmaximizes airflow through EMI gaskets to achieve maximum cooling whileproviding EMI isolation. The increased airflow disrupts the need forexotic thermal solutions (e.g., designed heat sinks, expensive/complexfaceplate design, high performance fans) to provide additional coolingas ASIC components evolve in density and heat production. The techniquesenable the reuse of common components (e.g., heatsinks, fans, etc.) fromlegacy platforms to the latest generation platform, which directlytranslates to higher volume production at a lower unit cost.Additionally, the overall system layout of top down linear integrationsequences enable the deployment of robotic automation to improve qualityand lower labor dependence, resulting in lower unit costs.

The EMI gasket design provides continuous effective contact between themetal chassis and the metal frame of ports extending from the chassis,while providing increased airflow through the perforations covering atleast 90% of the EMI gasket. The EMI gasket provides a cost effectivesolution that targets multiple challenges, such as cooling, EMIshielding, design for cost, design for automation and quality in highvolume system production.

In one form, an apparatus comprising a chassis, an upper EMI gasket, anda lower EMI gasket is provided. The chassis comprises an upper chassisand a lower chassis that are constructed from a conductive sheet with afirst thickness. The upper chassis and the lower chassis are coupled toform an interior of the chassis housing an electronic device. The upperEMI gasket is attached to the upper chassis, and has a second thicknessthat is less than the first thickness. The upper EMI gasket includesperforations to allow cooling air through the upper EMI gasket and intothe interior of the chassis. The lower EMI gasket is attached to thelower chassis, and also has a second thickness that is less than thefirst thickness. The lower EMI gasket includes perforations to allowcooling air through the lower EMI gasket and into the interior of thechassis. Both the upper EMI gasket and the lower EMI gasket areconfigured to resiliently contact a portion of the electronic device toprovide EMI shielding for the electronic device.

In another form, a system comprising a chassis, an electronic device, afan, an upper EMI gasket, and a lower EMI gasket is provided. Thechassis comprises an upper chassis and a lower chassis that areconstructed from a conductive sheet with a first thickness. Theelectronic device comprises a motherboard disposed in the interior ofthe chassis and a daughterboard including a plurality of portsaccessible from outside the chassis. The upper chassis and the lowerchassis are coupled to form an interior of the chassis housing anelectronic device. The fan is configured to draw cooling air into theinterior of the chassis and cool the electronic device. The upper EMIgasket is attached to the upper chassis, and has a second thickness thatis less than the first thickness. The upper EMI gasket includesperforations to allow the cooling air through the upper EMI gasket andinto the interior of the chassis. The lower EMI gasket is attached tothe lower chassis, and also has a second thickness that is less than thefirst thickness. The lower EMI gasket includes perforations to allow thecooling air through the lower EMI gasket and into the interior of thechassis. Both the upper EMI gasket and the lower EMI gasket areconfigured to resiliently contact the daughterboard to provide EMIshielding for the electronic device.

In still another form, a method for assembling an electronic devicewithin a chassis is provided. The method includes mounting theelectronic device on a lower chassis constructed of a conductive sheetof a first thickness. The method also includes attaching a lower EMIgasket to the lower chassis. The lower EMI gasket has a second thicknessthat is less than the first thickness. The lower EMI gasket alsoincludes perforations to allow cooling air through the lower EMI gasket.The method further includes attaching an upper EMI gasket having asecond thickness to an upper chassis having a first thickness. The upperEMI gasket also includes perforations to allow cooling air through theupper EMI gasket. The method also includes coupling the upper chassis tothe lower chassis to enclose the electronic device. When coupling theupper chassis and the lower chassis, the upper EMI gasket and the lowerEMI gasket are configured to resiliently contact a portion of theelectronic device to provide EMI shielding for the electronic device.

The descriptions of the various embodiments have been presented forpurposes of illustration, but are not intended to be exhaustive orlimited to the embodiments disclosed. Many modifications and variationswill be apparent to those of ordinary skill in the art without departingfrom the scope and spirit of the described embodiments. The terminologyused herein was chosen to best explain the principles of theembodiments, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

What is claimed is:
 1. An apparatus comprising: a chassis comprising anupper chassis and a lower chassis, the chassis constructed from aconductive sheet with a first thickness, wherein the upper chassis andthe lower chassis are coupled to form an interior of the chassis housingan electronic device; an upper Electro-Magnetic Interference (EMI)gasket attached to the upper chassis and resiliently contacting a firstportion of the electronic device, the upper EMI gasket having a secondthickness less than the first thickness, wherein the upper EMI gasketincludes perforations to allow cooling air through the upper EMI gasketand into the interior of the chassis; and a lower EMI gasket attached tothe lower chassis and resiliently contacting a second portion of theelectronic device, the lower EMI gasket being separate from the upperEMI gasket and having the second thickness, wherein the lower EMI gasketincludes perforations to allow cooling air through the lower EMI gasketand into the interior of the chassis, and wherein the upper EMI gasketand the lower EMI gasket are configured to provide EMI shielding for theelectronic device.
 2. The apparatus of claim 1, wherein the secondthickness of the upper EMI gasket and the lower EMI gasket allows theperforations to cover at least 90% of the upper EMI gasket and the lowerEMI gasket.
 3. The apparatus of claim 1, wherein the chassis includesstandoffs constructed from the conductive sheet with the firstthickness, the standoffs configured to provide structural support to theelectronic device.
 4. The apparatus of claim 3, further comprising oneor more fasteners that couple the upper chassis to the lower chassisthrough the standoffs.
 5. The apparatus of claim 4, wherein the one ormore fasteners are electrically conductive to provide additional EMIshielding for the electronic device.
 6. The apparatus of claim 3,wherein the upper EMI gasket is attached to the upper chassis throughlocking tabs coupled to slots in the standoffs.
 7. The apparatus ofclaim 1, wherein the lower EMI gasket is attached to the lower chassisby swaging a portion of the lower chassis to the lower EMI gasket.
 8. Asystem comprising: a chassis comprising an upper chassis and a lowerchassis, the chassis constructed from a conductive sheet with a firstthickness, wherein the upper chassis and the lower chassis are coupledto form an interior of the chassis; an electronic device comprising amotherboard disposed in the interior of the chassis and a daughterboardincluding a plurality of ports accessible from outside the chassis; afan to draw cooling air into the interior of the chassis and cool theelectronic device; an upper Electro-Magnetic Interference (EMI) gasketattached to the upper chassis, the upper EMI gasket having a secondthickness less than the first thickness, wherein the upper EMI gasketincludes perforations to allow the cooling air through the upper EMIgasket and into the interior of the chassis; and a lower EMI gasketattached to the lower chassis, the lower EMI gasket having the secondthickness, wherein the lower EMI gasket includes perforations to allowthe cooling air through the lower EMI gasket and into the interior ofthe chassis, and wherein the upper EMI gasket and the lower EMI gasketare configured to resiliently contact the daughterboard to provide EMIshielding for the electronic device.
 9. The system of claim 8, whereinthe second thickness of the upper EMI gasket and the lower EMI gasketallows the perforations to cover at least 90% of the upper EMI gasketand the lower EMI gasket.
 10. The system of claim 8, wherein the chassisincludes standoffs constructed from the conductive sheet with the firstthickness, the standoffs configured to provide structural support to thedaughterboard.
 11. The system of claim 10, further comprising one ormore fasteners that couple the upper chassis to the lower chassisthrough the standoffs.
 12. The system of claim 11, wherein the one ormore fasteners are electrically conductive to provide additional EMIshielding for the electronic device.
 13. The system of claim 10, whereinthe upper EMI gasket is attached to the upper chassis through lockingtabs coupled to slots in the standoffs.
 14. The system of claim 8,wherein the lower EMI gasket is attached to the lower chassis by swaginga portion of the lower chassis to the lower EMI gasket.
 15. A methodcomprising: mounting an electronic device on a lower chassis constructedof a conductive sheet of a first thickness; attaching a lowerElectro-Magnetic Interference (EMI) gasket to the lower chassis, thelower EMI gasket having a second thickness less than the firstthickness, wherein the lower EMI gasket includes perforations to allowcooling air through the lower EMI gasket; attaching an upper EMI gaskethaving the second thickness to an upper chassis having the firstthickness, wherein the upper EMI gasket is separate from the lower EMIgasket and includes perforations to allow cooling air through the upperEMI gasket; and coupling the upper chassis to the lower chassis toenclose the electronic device, wherein the upper EMI gasket isconfigured to resiliently contact a first portion of the electronicdevice and the lower EMI gasket is configured to resiliently contact asecond portion of the electronic device to provide EMI shielding for theelectronic device.
 16. The method of claim 15, further comprisingstamping the perforations in the upper EMI gasket and the lower EMIgasket to cover at least 90% of the upper EMI gasket and the lower EMIgasket.
 17. The method of claim 15, further comprising forming standoffsfrom the conductive sheet of the first thickness, the standoffsconfigured to provide structural support to the electronic device. 18.The method of claim 17, wherein coupling the upper chassis to the lowerchassis comprises fastening the upper chassis to the lower chassisthrough the standoffs.
 19. The method of claim 17, wherein attaching theupper EMI gasket to the upper chassis comprises inserting one or morelocking tabs formed in the upper EMI gasket into one or morecorresponding slots in the standoffs.
 20. The method of claim 15,wherein attaching the lower EMI gasket to the lower chassis comprisesswaging a portion of the lower chassis to the lower EMI gasket.